It was first mentioned in the episode Ricksy Business, but it first appeared in the episode Get Schwifty. It was seen in Get Schwifty when Morty used Rick's Portal gun, cycling through dimensions until Birdperson took him in and charged the Portal Gun.
Bird People live in wooden structures often incorporated into trees, but do possess technology like TV. They primarily eats worms and have worm ranches around on the planet. When sending messages they tend to use robotic eggs with hologram messages. In Bird culture, mate-melding is the equivalent of marriage on Earth.